A method of programming a flash memory device, which is a nonvolatile memory device including a plurality of pages, includes executing an Nth program loop of a program operation by applying an Nth selected program voltage to a selected word line from among the plurality of pages, and performing a program verify operation by applying a program verify voltage to the selected word line, counting the number of memory cells having a threshold voltage which is greater than or equal to the program verify voltage, from among memory cells connected to the selected word line, generating a program voltage revision value based on a result of the counting and an operational condition of the Nth program loop, and adding the program voltage revision value to an Mth preset program voltage of an Mth program loop executed after the Nth program loop where M>N.